This work presents a novel sensor setup for the general detection of liquid-liquid interfaces in different mixes of liquids as part of a liquid-liquid extraction device. The sensor setup is applied to a laboratory scale separatory funnel. It uses a near infrared sensor array which receives light going through the liquids inside the funnel, which are illuminated by a light source located on the other side and below the funnel. Light refracts inside the funnel and the liquids and reflects on the interface creating changing patterns in the light intensity measured by the sensor, providing a way of locating the liquid-liquid interface. Liquid mixes with different optical features, from transparent to opaque, emulsion and clean, are used to test whether different types of interfaces produce a distinguishable response on the sensor, allowing to detect interfaces in different situations that can occur as part of an Artificial Intelligence orchestrated battery chemical synthesis process. Emulsion interfaces create a discernible change in the sensor input by lowering the light intensity registered when crossing in front of the sensor making them easier to locate than with other optical techniques. The setup opens the possibility of detecting a liquid-liquid interface as it is forming and can be miniaturized to be attached to laboratory funnels as a manual aid or used with other transparent vessels in automatic solutions like liquid handling robots or pipetting robots.